This invention relates to a variable capacity vane compressor for compressing refrigerant gas circulating in an air conditioner installed on an automotive vehicle, or for like applications, and more particularly to a vane compressor of this kind the capacity of which can be controlled by an external control signal.
Conventionally, variable capacity vane compressors of this kind controllable by external control signals have been proposed, e.g. by Japanese Provisional Patent Publications (Kokai) Nos. 63-205478 and 63-85285, each of which comprises a control element disposed to rotate between the minimum capacity position and the maximum capacity position for controlling the timing of start of compression, a low-pressure chamber which is formed on one side of a pressure-receiving protuberance of the control element and into which is introduced suction pressure as low pressure, a high-pressure chamber formed on the other side of the pressure-receiving protuberance and into which is introduced discharge pressure as high pressure via a restriction passage to create control pressure therein, the control element being rotated in response to difference between the sum of the suction pressure introduced into the low-pressure chamber and the urging force of urging means, and the control pressure, and an electromagnetic valve for opening and closing a passageway which communicates between the high-pressure chamber and a suction chamber, wherein the opening and closing of the passageway by the electromagnetic valve is controlled by an external control signal supplied from the outside of the compressor to control the flow rate of refrigerant gas leaking from the high-pressure chamber into the suction chamber to vary the control pressure within the high-pressure chamber such that the control element is rotated in accordance with variation in the control pressure, to thereby control the capacity of the compressor in a continuous manner.
According to these prior art vane compressors, the passageway communicating between the high-pressure chamber and the suction chamber is opened and closed by the electromagnetic valve to vary the control pressure within a range of approx. 2 to 14 kg/cm.sup.2 so that the capacity of the compressor is continuously changed between the minimum and maximum values. Further the cross-sectional area of the passageway is large. More specifically, when the capacity of the compressor is the maximum, refrigerant gas under pressure as high as approx. 14 kg/cm.sup.2 acts on the electromagnetic valve, and moreover, the flow rate of refrigerant gas under such high pressure leaking from the high-pressure chamber into the suction chamber is controlled by opening and closing the passageway which has such a large cross-sectional area with the electromagnetic valve, which gives a heavy burden to the electromagnetic valve. Therefore, the electromagnetic valve has to be designed to have a strong valve-closing force (magnetically attractive force), which, however, results in an increased size of the electromagnetic valve.
Further, according to the prior art vane compressors, in order to control the capacity of the compressor in a fine manner by an external control signal from the outside, a large electromagnetic valve is required, which is excellent in responsiveness and capable of controlling a large amount of refrigerant gas.